Prospective comparison of indirect methods for detecting lactase deficiency.

To compare sensitivity, specificity and convenience, four indirect methods of detecting lactase deficiency were tested prospectively in 25 subjects with biopsy-proved lactase deficiency and in 25 with normal lactase activity. After ingestion of 50 g of lactose, containing 1-14Clactose, breath hydrogen was abnormally elevated in all 25 lactase-deficient subjects (greater than 0.30 ml per minute at two hours); breath 14CO2 was below the normal range in 23, and in 19 the plasma glucose increased by less than 20 mg per deciliter. When lactose and ethanol were given together, the rise in plasma galactose remained less than 5 mg per deciliter in 24 of the lactase-deficient subjects. The specificity of the four tests was excellent, with only one false-positive plasma glucose test. Measurement of breath hydrogen is sensitive and specific, and does not require ethanol or isotopes. It is noninvasive, and is not influenced by gastric emptying or metabolic factors. We believe it to be the most suitable test for population screening for lactase deficiency.